In radio transmitters, a transmission signal, i.e. the signal being transmitted, has to be amplified in to a level suitable for transmission over an air interface to a radio receiver. The level of the amplified transmission signal should be high enough to enable the radio receiver to decode information contained in the transmission signal.
CMOS (Complementary metal-oxide-semiconductor) transistors have been widely used in amplifiers implemented as integrated circuits. Advantages of the CMOS transistors over, for example, bipolar junction transistors (BJT) are obvious to one skilled in the art. Typical disadvantages of CMOS transistors in comparison with BJTs include, however, lower trans-conductance, lower breakdown voltage, limited performance of passive components in CMOS process, and lower isolation. A lower trans-conductance leads to a higher current consumption in an amplifier, a lower breakdown may result in a low power supply and, as a consequence, in a limited swing at an output of the amplifier. A limited passive component performance leads to lower integration level and designs that avoid use of resistors, for example. Lower isolation makes it harder to design a wide and accurate power tuning range. Consequently, there are problems in using CMOS transistors in amplifiers that must be accounted for.